In a process of depositing a film on a wafer in a processing container of a film forming apparatus, a film may adhere to the inside of the processing container in some cases. In such a process, for example, a film forming process of a metal film or an insulating film may be performed in some cases. When replacing a film-formed wafer with an unprocessed wafer after the film forming process, a plurality of particles may adhere to the surface of the wafer in the case of unloading the processed wafer or loading the unprocessed wafer. For example, there is known a technique for reducing the plurality of particles adhering to the wafer surface as described above.
In the prior art, a film forming apparatus that sequentially supplies plural types of reaction gases reacting with each other to a wafer in a processing container kept in a vacuum atmosphere performs a film forming process of a thin film formation and unloads a wafer. Thereafter, particles adhered to the portions making contact with the reaction gases are removed by the flow of a purge gas. The pressure of the purge gas is increased to above the pressure available at the time of pressurization of the reaction gases by using a pressurization-purpose storage tank for initially pressurizing the reaction gases and then discharging the reaction gases into the processing container. Thereafter, the purge gas is supplied into the processing container. Therefore, due to the strong flow of the purge gas, the particles existing in a flow path on the downstream side of the storage tank are caused to flow and are removed together with the purge gas. This makes it possible to reduce the particles adhering to the processing container.
Furthermore, in the prior art, a wafer boat holding wafers W mounted thereon is loaded into a reaction vessel. The interior of the reaction vessel is set to a vacuum atmosphere. Then, a dichlorosilane gas is pressurized in a storage tank. Thereafter, a film forming process of a SiN film is performed by alternately performing a step of supplying the dichlorosilane gas to the reaction vessel and a step of supplying an ammonia gas to the reaction vessel. Next, the wafer boat is unloaded from the reaction vessel, the reaction vessel is closed with a lid, and a purging step is performed. In the purging step, the temperature of the reaction vessel is raised and then lowered. During the temperature lowering, an operation of storing and pressurizing a purge gas in a storage tank and discharging the purge gas to the reaction vessel is repeated a plurality of times. As a result, the thin film adhering to the inside of the reaction vessel is forcibly peeled off, and the particles existing in the flow path of the dichlorosilane gas are removed. This makes it possible to reduce particle contamination of the wafers W.
As described above, various purging processes for supplying a purge gas into a reaction vessel at a relatively high pressure have been developed so far in order to reduce particle contamination. However, a demand has existed for a technique regarding a purging process for more sufficiently reducing particle contamination.